<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        p{
            color:blue;
        }
        .num_one{
            color:red;
        }
        .num_two{
            color:green;
        }
        .size{
            font-size:30px;
        }
    </style>
</head>
<body>
    <p>你好呀</p>
    <p class="num_one">你好呀</p>
    <p class="num_two">你好呀</p>
    <h1 class="num_one size">我很开心</h1>
</body>
</html>